Biomedical subjects

E A Lachica

Publications and source records attributed to E A Lachica.

17 recordsLinked to original sources

PubMed1998

Glutamatergic and GABAergic agonists increase [Ca2+]i in avian cochlear nucleus neurons.

Neurons of the avian cochlear nucleus, nucleus magnocellularis (NM), are stimulated by glutamate, released from the auditory nerve, and GABA, released from both interneurons surrounding NM and from cells located in the superior olivary nucleus. In this study, the Ca2+ indicator dye Fura-2 was used to measure Ca2+ responses in NM stimulated by glutamate- and GABA-receptor agonists using a chicken brainstem slice preparation. Glutamatergically stimulated Ca2+ responses were evoked by kainic acid (KA), alpha-amino-3-hydroxyl-5-methylisoxazole-4-propionic acid (AMPA), and N-methyl-D-aspartate (NMDA). KA- and AMPA-stimulated changes in [Ca2+]i were also produced in NM neurons stimulated in the presence of nifedipine, an L-type Ca2+ channel blocker, suggesting that KA- and AMPA-stimulated changes in [Ca2+]i were carried by Ca2(+)-permeable receptor channels. Significantly smaller changes in [Ca2+]i were produced by NMDA. When neurons were stimulated in an alkaline (pH 7.8) superfusate, NMDA responses were potentiated. KA- and AMPA-stimulated responses were not affected by pH. Several agents known to stimulate metabotropic receptors in other systems were tested on NM neurons bathed in a Ca2+ free-EGTA--buffered media, including L-cysteine sulfinic acid (L-CSA), trans-azetidine dicarboxylic acid (t-ADA), trans-aminocyclo-pentanedicarboxylic acid (t-ACPD), and homobromoibotenic acid (HBI). The only agent to reliably and dose-dependently increase [Ca2+]i was HBI, an analog of ibotenate. GABA also stimulated increases in [Ca2+]i in NM neurons. GABA-stimulated responses were reduced by agents that block voltage-operated channels and by agents that inhibit Ca2+ release from intracellular stores. Whereas GABA-A receptor agonist produced increases in [Ca2+]i GABA-B and GABA-C receptor agonists had no effect. There appear to be several ways for [Ca2+]i to increase in NM neurons. Presumably, each route represents a means by which Ca2+ can alter cellular processes.

Animals↗

PubMed1997

Mitochondrial regulation of calcium in the avian cochlear nucleus.

The role of mitochondria and the endoplasmic reticulum in buffering [Ca2+]i in response to imposed calcium loads in neurons of the chick cochlear nucleus, nucleus magnocellularis (NM), was examined. Intracellular calcium concentrations were measured using fluorometric videomicroscopy. After depolarization with 125 mM KCl, NM neurons demonstrate an increase in [Ca2+]i that returns to near-basal levels within 6 min. Addition of the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP) dissipated the mitochondrial membrane potential, as evidenced by increased fluorescence when cells were loaded with rhodamine-123. Two micromolar CCCP had minimal effect on baseline [Ca2+]i. However, 2 or 10 microM CCCP interfered with the ability of NM cells to buffer [Ca2+]i in response to KCl depolarization without significantly affecting peak [Ca2+]i. Oligomycin also interfered with postdepolarization regulation of [Ca2+]i, but blocked late (7-8 min postdepolarization) increases in [Ca2+]i caused by CCCP. Thapsigargin had no effect on baseline, peak, or postdepolarization [Ca2+]i in NM cells. These results suggest that normal mitochondrial membrane potential and ATP synthesis play an important role in buffering [Ca2+]i in response to imposed calcium loads in NM neurons. Furthermore, the endoplasmic reticulum does not appear to play a significant role in either of these processes. Thus increases in mitochondrial number and function noted in NM cells after deafferentation may represent an adaptive response to an increased cytosolic calcium load.

Animals↗

PubMed1996

Glutamate modulates intracellular Ca2+ stores in brain stem auditory neurons.

1. Fura-2 imaging was used to measure the effects of glutamate on caffeine-sensitive Ca2+ stores in neurons of the avian cochlear nucleus, n. magnocellularis (NM). 2. On average, 100-mM caffeine stimulated a 250-nM increase in intracellular calcium ion concentration {[Ca2+]i} in Ca(2+)-free media; 1-mM glutamate significantly attenuated caffeine-stimulated Ca2+ responses. 3. The metabotropic glutamate receptor agonist, ACPD, also inhibited the caffeine-stimulated rise in [Ca2+]i. 4. Glutamate has an important role in regulating Ca2+ stores in NM neurons. Glutamate-deprivation (viz. cochlear removal) results in a rise in [Ca2+]i that may, in part, be the result of release from Ca2+ stores. We hypothesize that Ca(2+)-induced Ca2+ release stores (CICRs) may be involved in deprivation-induced cell death.

Animals↗

PubMed1995

Deafferentation increases the intracellular calcium of cochlear nucleus neurons in the embryonic chick.

1. Ratiometric fura-2 imaging was used to measure the intracellular calcium concentration ([Ca2+]i) of neurons in the embryonic avian cochlear nucleus, nucleus magnocellularis (NM), after an in ovo unilateral cochlea removal (deafferentation). 2. The mean [Ca2+]i of NM neurons receiving normal input was 113 nM. 3. Deafferentation increased the mean [Ca2+]i of NM neurons to 247, 311, 339, and 314 nM at 1, 3, 6, and 12 h after cochlear removal, respectively. These values did not differ significantly. 4. The percent frequency distribution of deafferented NM neuron [Ca2+]i shifts away from normative levels toward higher [Ca2+]i at 1 and 3 h after cochlear removal, but shifts back toward normative levels at 6 and 12 h after cochlear removal. 5. This increased [Ca2+]i following cochlear removal temporally coincides with well-characterized changes in NM neurons following activity deprivation. 6. These data suggest that deregulation of [Ca2+]i homeostasis plays a key role in NM neuron degeneration and death following activity deprivation.

Animals↗

PubMed1995

Activation of a metabotropic glutamate receptor increases intracellular calcium concentrations in neurons of the avian cochlear nucleus.

Metabotropic glutamate receptors have been shown to stimulate phosphatidylinositol metabolism, and subsequently liberate Ca2+ from intracellular stores, in a variety of tissue and cell types. We previously demonstrated that glutamate could stimulate phosphatidylinositol metabolism, generating inositol-1,4,5-trisphosphate (IP3), in isolated cochlear nucleus tissue from the chick. Using the calcium indicator dye fura-2 and ratiometric fluorescent imaging, this study examined the ability of glutamate and its analogs to liberate Ca2+ from intracellular stores of neurons of the avian cochlear nucleus, and qualitatively characterized the pharmacological profile of such an action. In normal, Ca(2+)-containing medium, glutamate, kainate (KA), alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), NMDA, quisqualate (QUIS), and (+/-)-aminocyclopentane-trans-dicarboxylate (ACPD) elicited increases in intracellular calcium concentrations ([Ca2+]i). In the absence of external Ca2+, glutamate, quisqualate, and ACPD evoked increases in [Ca2+]i. In normal medium, the ionotropic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and the NMDA receptor antagonist 2-amino-5-phosphonovalerate (APV) attenuated but did not abolish the glutamate-evoked response and had no effect on the ACPD-evoked response. The putative metabotropic glutamate receptor antagonist 2-amino-3-phosphonopropionate (AP3) was without effect on the glutamate- and ACPD-evoked increases in [Ca2+]i in Ca(2+)-free medium. We conclude that a metabotropic glutamate receptor (mGluR) is present on cochlear nucleus neurons and is able to stimulate the phosphatidylinositol metabolism--Ca2+ signal transduction cascade.

Animals↗

PubMed1995

Glutamatergic inhibition of voltage-operated calcium channels in the avian cochlear nucleus.

The auditory nerve serves as the only excitatory input to neurons in the avian cochlear nucleus, nucleus magnocellularis (NM). NM neurons in immature animals are dependent upon auditory nerve signals; when deprived of them, many NM neurons die, and the rest atrophy. Auditory nerve terminals release glutamate, which can stimulate second messenger systems by activating a metabotropic glutamate receptor (mGluR). Therefore, it is possible that the effectors of mGluR-stimulated signal transduction systems are needed for NM neuronal survival. This study shows that mGluR activation in NM neurons attenuates voltage-dependent changes in [Ca2+]j. Voltage-dependent Ca2+ influx was also attenuated by increasing cAMP with forskolin, VIP, or 8-bromo-cAMP, indicating that mGluR activation may stimulate adenylate cyclase. The main results may be summarized as follows. NM neurons possess high voltage-activated Ca2+ channels that were modulated by quisqualate, glutamate, and (+/-)trans-ACPD, in that order of potency. Glutamatergic inhibition of Ca2+ influx was not blocked by L-AP3 or L-AP4, which antagonize the actions of mGluRs in other neural systems; it was blocked by serine-O-phosphate. Finally, the attenuation of voltage-dependent Ca2+ influx was duplicated by cAMP accumulators. Since NM neurons have high rates of spontaneous activity and higher rates of driven activity, the expression of this mGluR turns out to be very valuable: without it, [Ca2+]j could reach lethal concentrations. These results provide an important clue as to the identity of an intracellular signal that may play an important role in NM neuronal survival.

Animals↗

PubMed1994

GABAergic terminals in nucleus magnocellularis and laminaris originate from the superior olivary nucleus.

The auditory brainstem nuclei, angularis (NA), magnocellularis (NM), and laminaris (NL) of the chicken, Gallus, contain terminals that stain for antibodies against the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). Some of these terminals originate from cells surrounding nucleus magnocellularis. Results from this study indicate that the majority of the GABAergic terminals found in NA, NM and NL originate from the superior olivary nucleus (SON). Injections of cholera toxin and horseradish peroxidase show that superior olivary nucleus (SON) neurons, which respond to pure tones, project bilaterally to NA, NM, and NL. NA and NL are reciprocally connected with the SON. More NA cells project to the SON than NL cells. While SON neurons project to NM, NM neurons do not project axons back to the SON. The configuration of SON terminals in NA, NM and NL matches the pattern of GABA-immunoreactive puncta seen in these three nuclei: they surround individual NM cells, congregate in the dendritic neuropil of NL, and blanket the NA. The data indicate that NA, NM and NL may be affected by two different inhibitory cell types: local interneurons and SON neurons. Patterns of connectivity described in this report suggest that the activity of NA cells could influence NM and NL cell physiology. Specifically, increases in NA cell activity could augment the effects of GABAergic SON neurons on NM and NL. Hence, binaural perception in the chicken may be more dependent upon changes in intensity cues than previously believed.

Acoustic Stimulation↗

PubMed1993

Intrinsic connections of layer III of striate cortex in squirrel monkey and bush baby: correlations with patterns of cytochrome oxidase.

This study used biocytin and horseradish peroxidase (HRP) to examine the intrinsic connections of the cytochrome oxidase (CO) rich blob and CO poor nonblob zones within layer III of striate cortex in two primate species, nocturnal prosimian bush babies (Galago crassicaudatus) and diurnal simian squirrel monkeys (Saimiri sciureus). Our main objective was to determine whether separate classes of lateral geniculate nucleus (LGN) cells projected to separate superficial layer zones or layers in either species. There were three significant findings. First, we confirm that layer III consists of three sublayers, IIIA, IIIB, and IIIC in both species. Layer IIIA receives input from layers IIIB, IIIC, and V, with little or no input from LGN recipient layers IV and VI. Layer IIIB receives its input from nearly every cortical layer. Layer IIIC, receives input principally from layers IV alpha [which receives its input from magnocellular (M) LGN cells] and from layers V and VI. Taken together with other findings on the extrinsic connections of these layers, our data suggest that IIIA and IIIC provide output to separate hierarchies of visual areas and IIIB acts as a set of interneurons. Second, we find that, as in macaque monkeys, cells in both IV beta and IV alpha of bush babies and squirrel monkeys project to layer IIIB, converging within the blobs. These results suggest that information from all LGN cell classes [parvocellular (P), M, and the Koniocellular (K) or their equivalents] may be integrated within the blobs. Thus, blobs in all of these primates may perform a function that transcends visual niche differences. Third, our data show a species specific difference in the connections of the IIIB nonblobs; nonblobs receive indirect input via IV alpha from the LGN M pathway in bush babies but receive indirect input via IV beta from the LGN parvocellular (P) pathway in squirrel monkeys. These findings indicate that the role of nonblob zones within striate cortex differs from that of blob zones and takes into account visual niche differences.

Animals↗

PubMed1992

Direct W-like geniculate projections to the cytochrome oxidase (CO) blobs in primate visual cortex: axon morphology.

The primate lateral geniculate nucleus (LGN) is composed of large, medium, and small cells located, respectively, in magnocellular (M), parvocellular (P), and specialized layers (intercalated and S-layers in simians, koniocellular (K) layers in prosimians). Several studies have examined the physiology and connections of M and P LGN cells and have concluded that they provide separate contributions to visual perception via separate pathways. Less is known about the structure and contributions of the small LGN cells. This study examined the distribution and structure of K LGN cell axons in the cortex of the prosimian, Galago crassicaudatus. Wheat germ agglutinin conjugated to horseradish peroxidase, or Phaseonlus vulgaris leucoaglutinin, was injected into the LGN K layers to demonstrate the overall axon projection pattern and the details of individual axons, respectively. Location of axons within striate cortex was specified relative to boundaries determined by Nissl or cytochrome oxidase (CO) stains on the same or adjacent sections. Our results show that K LGN axons end as single complex arbors within one CO blob zone in layer III; they never terminate in interblob zones. These axons also emit a collateral in layer I that arborizes more broadly and spans both CO blob and interblob zones. These data, together with data on K cell physiology and intralaminar cortical connections, suggest that the LGN small cell pathway could modulate the activity of the other two pathways in striate cortex and contribute directly to visual perception.

Animals↗

PubMed1992

Parallel pathways in macaque monkey striate cortex: anatomically defined columns in layer III.

Visual information reaching striate cortex comes from parallel pathways, and the information is organized, or processed, by the layers and columns of striate cortex. To better understand how this is accomplished anatomically, we asked whether parallel pathways originating in the lateral geniculate nucleus (LGN), and terminating separately in layer IV, remain separate in layer III of macaque monkeys. Layer III is of interest since it may play a special role in color and form vision but not in analysis of visual motion. The chief finding was that cells in "blobs" of layer III that stain densely for cytochrome oxidase receive indirect input, via layer IVC, from both LGN magnocellular (M) and parvocellular (P) cells. This is important because the P and M pathways may represent color/form and motion-processing channels, respectively. Interblob cells receive indirect input, via layers IVC and IVA, from the LGN P cells. Also, as suggested by others, our data demonstrate that layer III can be subdivided. The bottom tier, layer IIIB, receives direct projections from all cortical layers. Output from layer IIIB appears to remain intrinsic to striate cortex. In contrast, the top tier, layer IIIA, receives projections from layer IIIB as well as from layers IVA, IVB (blobs only), and V, but it receives no direct projections from LGN recipient layers IVC and VI. Unlike layer IIIB, the output of layer IIIA reaches extrastriate areas. Thus, impulses arriving from parallel LGN pathways may be recombined through serial stages in striate cortex to produce a set of parallel pathways that are qualitatively different from the original LGN set.

Animals↗

PubMed1991

Morphological details of primate axons and dendrites revealed by extracellular injection of biocytin: an economic and reliable alternative to PHA-L.

The objective of this study was to determine if biocytin would reliably label details of distant axons and dendrites when injected extracellularly in primates. Biocytin (2.5-5%) was injected iontophoretically or by pressure into several areas of the visual and somatosensory systems of macaque monkeys, squirrel monkeys, tree shrews and galagos. After survival times that ranged from 9 h to 2 weeks, fine details of anterogradely filled axons and/or retrogradely filled dendrites were reliably revealed with an avidin-biotin-HRP complex (ABC solution) that was enhanced with heavy metals. Biocytin labeling was successfully combined with choline acetyltransferase (ChAT) or cytochrome oxidase (CO) histochemistry to reveal double-labeled cells. Our results show that biocytin is a versatile, easy-to-use label that completely fills cell processes both anterogradely and retrogradely in several primate species.

Animals↗

PubMed1990

Effects of monocular deprivation on the morphology of retinogeniculate axon arbors in a primate.

Previous studies of the monocularly deprived (lid-sutured) primate (Galago crassicaudatus) have shown that magnocellular (M) and parvocellular (P) lateral geniculate nucleus (LGN) cells that receive input from the deprived eye are smaller than counterparts that receive input from the nondeprived eye; deprived koniocellular (K) cells show wide variability in size, but they do not differ from their nondeprived counterparts (Casagrande and Joseph, '80). Although deprivation results in cell-size changes, the physiological properties of deprived LGN cells do not change from normal (that is, P cells have normal X-like properties, M cells have normal Y-like properties, and K cells have normal W-like properties). Because of these findings, we were interested in determining how the morphology of retinogeniculate axon arbors is affected by deprivation. To this end, 104 horseradish-peroxidase-filled retinogeniculate arbors from galagos deprived from birth to maturity were completely reconstructed within the binocular segment of the LGN. These arbors were qualitatively and quantitatively compared with 56 arbors reconstructed from normal galagos as part of another study (Lachica and Casagrande, '88). Our main findings are as follows. Deprived M and P arbors are affected by deprivation in the same general manner: compared with normal arbors, they are altered in shape (rather than being round or columnar, respectively, both groups have terminals that are elongated parallel to laminar borders); they are smaller in area, and they have fewer boutons but innervate the LGN with a greater density of boutons. K arbors are affected by deprivation in the same manner, but less severely. Finally, our results show that nondeprived arbors are also affected by eyelid suture. Specifically, all nondeprived arbor groups are smaller in area than normal and possess more boutons/mm3. We interpret these changes in the morphology of deprived retinogeniculate axons to suggest that abnormal competitive interactions begin by affecting primarily immature LGN cells and their axons and that the retinogeniculate axons presynaptic to these cells experience secondary degenerative effects. Our results also show that similar manipulations of visual experience can result in changes that are not necessarily comparable across species such as cats and primates.

Animals↗

PubMed1988

Development of primate retinogeniculate axon arbors.

In this study we examine the postnatal development of retinogeniculate axons projecting to the magnocellular (M axons), parvocellular (P axons), and koniocellular (K axons) layers of the lateral geniculate nucleus (LGN) in the prosimian primate, Galago crassicaudatus, in order to: (1) understand how individual retinogeniculate axons in primates mature postnatally, and (2) determine whether differences exist in the development of separate classes of axons that are known to be presynaptic to physiologically distinct cells in adults. In galagos, magnocellular, parvocellular, and koniocellular LGN layers contain Y-, X-, and W-like physiological cell classes, respectively (Norton & Casagrande, 1982). In vitro and in vivo optic tract bulk injections of horseradish peroxidase (HRP) were made in animals ranging in age from the day of birth (P0) to adulthood. Two hundred and fifty axonal arbors were completely reconstructed from serial sections and examined qualitatively for general features of maturity and compared quantitatively for changes in shape, arbor width, area, volume, bouton number, and bouton density. Our results confirm that in adult galagos M arbors are large and radially symmetric; P arbors are medium sized and elongated perpendicular to layer borders; K arbors are small and generally oriented parallel to layer borders. At birth, M, P, and K arbors, although still distinct and confined to layers, are qualitatively and quantitatively immature. Both the pattern and pace of maturation differ between classes. Overall, M arbors mature before P arbors which in turn mature before K arbors. Within classes, arbors representing central vision appear to develop about a week ahead of those representing peripheral vision; no differences are evident between the development of crossed and uncrossed arbors. In no case do arbors exhibit a period of postnatal exuberance, wherein arbors are larger than those of the adult as reported for cat X retinal axons. However, in width and bouton density P arbors are mature at P0 and thus occupy relatively more space in the nucleus compared to adult. All arbors mature rapidly and appear adult-like by the 4th or 5th postnatal week.

Animals↗

PubMed1987

Development of cytochrome oxidase staining in the retina and lateral geniculate nucleus: a possible correlate of ON- and OFF-center channel maturation.

A histochemical stain for cytochrome oxidase (CO) activity was used to examine the maturation of a neurochemical correlate of ON and OFF channels in the retina and dorsal lateral geniculate nucleus (LGN) of the tree shrew. In the adult tree shrew, the CO staining pattern can be used as a histochemical marker of segregated ON- and OFF-center channels in the retina, LGN, and striate cortex. Our previous studies have shown that the retina is immature and the LGN unlaminated at birth. In the present study, we show that the laminar development of CO reactivity emerges during the first postnatal week in the LGN, while the maturation of CO staining in the presumed ON and OFF sublaminae of the retinal inner plexiform layer develops slowly, well after the appearance of differential laminar CO staining in the LGN.

Animals↗

PubMed1986

Laminar asymmetry in the distribution of choline acetyltransferase-immunoreactive neurons in the retina of the tree shrew (Tupaia belangeri).

Cholinergic neurons in the retina of the tree shrew were identified immunocytochemically using a monoclonal antibody directed against choline acetyltransferase (ChAT). The chief result is that roughly 4 times as many ChAT-immunoreactive neurons are found in the inner nuclear layer (INL) as in the ganglion cell layer (GCL). In the INL, two classes of cholinergic neuron can be distinguished on the basis of soma size, one large and one small. The large neurons correspond closely in size and number to the displaced cholinergic neurons in the GCL, suggesting that these are the matching populations of cholinergic amacrine cells reported in other species. The small ChAT-immunoreactive neurons, on the other hand, which make up 60% of the total number of ChAT-positive neurons in the retina, appear to have no counterpart in the GCL. Whether these small neurons are a separate class of amacrine cell or some other cell type (e.g. bipolar, interplexiform, etc.) remains to be determined.

Animals↗

PubMed1985

Demonstration of ipsilateral retinocollicular projections in the tree shrew (Tupaia glis).

Ipsilateral retinocollicular projections labeled by anterograde transport of wheatgerm agglutinin-horseradish peroxidase (HRP) conjugate in the tree shrew were examined. For those animals in which this pathway was demonstrated (4 of 14) ipsilateral collicular labeling extended across approximately the anterior two-thirds of the colliculus, with the exception of the extreme rostral pole. Labeling was invariably punctuate and spaced at regular intervals in the lower stratum griseum superficiale. The laminar distribution and patchy terminations of ipsilateral projections are discussed in relation to two apparently independent pathways originating in the temporal retina, the crossed and uncrossed collicular pathways.

Animals↗

PubMedDate not supplied

The morphology of collicular and retinal axons ending on small relay (W-like) cells of the primate lateral geniculate nucleus.

The lateral geniculate nucleus (LGN) of every primate examined contains a set of small relay cells in addition to separate sets of magnocellular and parvocellular relay cells. These small cells receive a direct retinal projection, and an indirect retinal projection via the superior colliculus (SC). Receptive-field analyses of the small LGN cells in the bush baby, a lorisiform primate, indicate that this cell class is composed of subclasses, similar in physiology to cat W cells. In an effort to identify some of these subclasses, we have examined the morphological features of retinal and collicular axonal arbors that end on small W-like cells in the LGN of the bush baby, Galago crassicaudatus. Small cells in this species are found in a prominent pair of koniocellular (K) layers as well as the interlaminar zones (ILZs). Retinal arbors were examined by bulk iontophoretic injection of horseradish peroxidase into the optic tract. Collicular arbors were filled via iontophoretic injection of biocytin into the superficial layers of the SC. Forty-eight axon arbors were completely reconstructed and quantitatively evaluated. Our findings show that retinal and collicular axon terminals differ in morphology on the basis of a number of criteria. Our analyses also suggest that retinal axons may have a stronger influence on K cells and collicular axons have a stronger influence of ILZ cells. The ramifications of these findings are provocative since these small LGN cells are known to project directly to the cytochrome-oxidase (CO) blobs within striate cortex. This relationship suggests that CO blob cells receive complex visual input not only from magnocellular and parvocellular LGN cells, but also from small cell pathways that are differentially influenced by retinal and collicular cells.

Animals↗